1. Field of the Invention
The present invention relates to a self-administration device and, more particularly, to a device for administrating a liquid drug to a patient's body by himself, used solely or in combination with a system for continuous administration of a microdose of a liquid drug such as analgetic or anesthetic agent, to allay pains such as postoperative pain, cancerous pain or the like.
2. Description of the Background Art
In the recent anesthetic field, there has been used continuous epidural anesthesia or epidural catheterization with a continuous microinjector to allay the pain of a patient such as postoperative pain, cancerous pain or the like. However, patient sometimes has unique symptoms and occasionally complains of a sudden pain even in the middle of continuous administration of a microdose of analgesics. In order to cope with such a critical moment, there have been developed devices for administering a dose of an analgesic by a patient. One example of such devices is a patient-controlled analgesic delivery device disclosed in Japanese national publication 63-501195 corresponding to international publication No. WO 87/00758.
The patient's controlled analgesic delivery device of the above prior art comprises a dose reservoir 90 defined by a raised plateau 98 of a back plate 86 and a circular flexible sheet 96 as illustrated in FIG. 5. The dose reservoir 90 is connected to first and second conduits each being communicated with a medical container or a catheter. The above device further comprises a floating plate 100 rested on the flexible sheet 96, and a push button 84 arranged above the floating plate 100. The push button 84 is pivoted at its base on a pin 116 and biased by a coil spring 124 mounted around the pin 116.
If the push button 84 is pushed downward by a finger of a patient, the dose reservoir 90 is pressed by the floating plate 100 and the liquid drug in the dose reservoir 90 is delivered to the body of the patient through the conduit as illustrated in FIGS. 5B and 5C. If the finger is released from the push button 84, the button 84 is returned to its original state by the coil spring 124 as illustrated in FIG. 5D.
In the above device, however, the flexible sheet 96 is scarcely restored to its original state by itself because of its poor restoring force even when the push button 84 is released from the pushing force and returned to its original state as shown in FIG. 5D. Thus, the dose reservoir 90 can be restored to its original state only when the flexible sheet 96 is filled out by a fresh liquid drug introduced into the dose reservoir 90 from a medical container. However, the medical container is so designed as to send out a microdosage of the liquid drug by a restoring force of a balloon. Thus, it takes a long time to fill up the dose reservoir 90 because of a low pumping rate of the medical container for microdose administration. For this reason, it is difficult with the self-administration device of the prior art to administer an additional dose of the liquid drug in short order because of a long refilling time.
Further, the self-administration device of the prior art is limited in dosage by the predetermined fixed volume of the dose reservoir, thus making it impossible to administer any desired dosage of the liquid drug in the critical moment. Another problem is that, as can be seen from FIG. 5, the self-administration device of the prior art is very complex in structure and high in production cost. Further, there is a fear of leakage of the liquid drug from the circumference of the flexible sheet 96.